water hammer from 3 port

[mitchellcook]

Evening all. Changed a mid position valve today because it was letting by to the cylinder and the h/w temp was reaching 80c. I thought nice easy one, bunged system and changed both body and head. Fired it up and was getting water hammer when c/h switches off. So I turned pump down to 1 and opened the gate valve bypass fully open (only 15mm). It still done it, so I had another valve body in the van and I changed it again. Surprise surprise, there's still water hammer. Any ideas/experience going? Thanks.

 

[villa_tom]

Are you definitely fitting it the right way round?

I've only ever had this before when I fit the valve wrong, it made a horrible racket and frightened the life out of me

 

[diamondgas]

One big 'clunk' or the machine gun effect? Is there a 'balancing' valve on the hot water circuit? My thoughts being that the flow through the hot water circuit's restricted? Where's the bypass tee'd in?

 

[mitchellcook]

yeah it's definitely fitted the right way tom. The valve's made by grasslin. A bit stumped atm

 

[lgastec]

My thoughts exactly dimondgas. Got called out once for a report of a banging noise when the heating went off. Turned out to be to much restriction on cylinder balancing valve. Hope this helps.

 

[Rickster123]

Sounds to me like an air lock whilst refilling the system. System overheating and giving the banging noise.

 

[mitchellcook]

It's more just one clunk when the head controls the body. tried turn the spindle manually and it does machine gun sometimes.

There is a gate valve on the cylinder return (which i fully opened) but they have also plumbed it in 15mm.

The bypass is where it should be also in 15mm with a g/v (fully open). The bypass and cylinder return both tee into each other but it stays 15mm. So the return is only 15mm above floor level, not exactly ideal, god knows at what point it goes to 22mm

 

[Rickster123]

Was it making the banging noise before you started?

 

[mitchellcook]

not that I was aware of.

 

[Rickster123]

not that I was aware of.

Then without sounding like a git it must be something you've done mate. Have you altered other valves? Did you fully vent the system?

 

[mitchellcook]

Vented system through rads and pump, didn't sound like there was much air in the system. Yeah i dont want to say to the customer i need to change pipework and then hear the classic ' It was fine before though'. It was only a cheapy grasslin 3 port. First time i've used one, half the price of honeywell. Think i might be back tomorrow honeywell in hand lol.

 

[buckley plumb]

if all fails replace valve with the non ball type like a myson it has a shaft with a hole cut into it so no ball and spring to hammer

 

[stevetheplumber]

the gate valve on the cylinder return are you sure it was fully open before ? usually they are only open a little way to restict the flow as a rule of thumb close it and open till you hear low through and then a quarter turn further

 

[mitchellcook]

Yeah it was fully open steve. It's only a 15mm return off the cylinder as well. Thinking about it now, there was no vent for the coil. Do you reckon there could be trapped air in the coil and that's causing the valve to hammer? or just poor build quality valve. Have any of you guys had this issue due to cheap mid-pos valve. think it was like £40

 

[Vee]

Reason for failure of three port and hammer sounds like lack of bypass / flow. Undersized pipework for strength of pump. High resistance in pipework either due to too small or blockage (cold feed?). Now valve renewed insufficient leakage which was helping as bypass is causing hammer as actually shutting off valve. Valve will fail again if underlying issue is not addressed.

 

[mitchellcook]

Just an update incase anyone else comes across this in the future. Changed to a danfoss paddle type and all is ok. Thanks for advice fellas